Reinforced shadow mask for colored tv picture tubes

ABSTRACT

A shadow mask for color TV picture tubes contains the conventional foraminous or translucent area formed by a multitude of miniature apertures in a curved portion of a thin metal sheet through which the electron beams pass in traveling from the electron guns at the rear of the tube to the viewing face at the front of the tube. Around the translucent area is an imperforate section formed into a wall and a flange and containing strengthening ribs. A reinforcing ring rigidly attached to the flange provides additional stability. Ordinarily, the mask assembly is mounted to the glass bulb of the picture tube by metal, spring-like members which are attached to the wall of the mask.

ite States Patent Kirchner Mar. 27, 1973 REINFORCED SHADOW MASK FOR2,897,392 7/1959 Fiore ..313/85 S COLORED TV PICTURE TUBES 3,404,302lO/l968 Nicklas ..3 l3/85 S [75] lnventor: Myron C. Kirchner, ltasco,lll. Primary mminer chafles W. Lanham [73] Assignee: Tubal Industries,'Inc., Elk Grove Assistant ExaminerJa.mes W. Davie Village, 111.Att0mey'-Stryker & Jacobson [22] Filed: Apr. 19, 1971 [57] ABSTRACT I{211 App! 135307 A shadow mask for color TV picture tubes containsRelated Application Data the conventional foraminous or translucent areai formed by a multitude of miniature apertures in a [62] g 1969' curvedportion of a thin metal sheet through which the 3 electron beams pass intraveling from the electron guns at the rear of the tube to the viewingface at the (gl ..29/25 .11,H30113j/g/5o(s) from of the tube. Around thetranslucent area is an {58] Fie'ld 4 25 imperforate section formed intoa wall and a flange 7' and containing strengthening ribs. A reinforcingring rigidly attached to the flange provides additional stability.OrdinarilyQthe mask assembly is mounted to the [56] References Citedglass bulb of the picture tube by metal, spring-like UNITED STATESPATENTS members which are attached to the wall of the mask.

3,479,546 6/1968 Mearsm ..3l3/85 s 2 Claims, 5 Drawing Figures i ""Hlu in I I Q/IIIIIIIIIIIIIIIIIIIlIIIIIIIIl/ INVENTOR MY/PO/V C. K/RCHNERREINFORCED SHADOW MASK FOR COLORED TV PICTURE TUBES This application isa division of U.S. application, Ser. No. 822,792, now U.S. Pat. No.3,639,799.

BACKGROUND OF THE INVENTION 1. Field of the Invention that during normalhandling, such as when the mask is inserted and removed during theprocess of forming the phosphor dots on the face of the picture tube,there is no substantial shift in location of the tiny apertures so 5that they return each time to the same location.

This invention is used in the construction of colored ing ring is tostabilize the mask. But it and its associated hardware became asubstantial portion of the mass of the mask assembly. This technique notonly makes the mask assembly costly and quite heavy, but also, becauseof the mass involved, there is usually produced a fairly largetemperature gradient in the assembly before it is able to reach auniform ambient temperature level. This usually requires a considerableamount of operational time. The temperature gradientr'esults in somewarping or twisting of the face of the mask which adversely affects theregistration of the mask apertures with respect to the phosphor dots onthe face of the picture tube and the electron beams from the gunslocated at the rear of the tube. Recently, attempts have been made toeliminate the traditional mounting ring assembly with its inherentdisadvantages. An example of this is a type of shadow mask described inU.S. Pat. No. 3,376,451. Although these recent innovations have beensomewhat successful, they still have had some drawbacks, primarilyin'the area of mechanical stability. Therefore, they have not been acceptedby the colored TV industry to the extent desired.

SUMMARY The present invention, which is sometimes referred to as auniframe mask, is somewhat of a variation and modification of theaperture mask described in the aforementioned patent. It contains theconventional curved translucent area "surrounded by an imperforatesection which bends back to form a rearwardly extending wall andterminating with an inward extending flange from the rear edge of thewall. A circumambient groove around the translucent area provides afirst strengthening rib and a continuous groove in the wall sectionprovides additional strengthening. Further strengthening can be providedby cross ribs in the wall section which may be extended onto the flangearea. A metal ring or annulus is rigidly attached to the flange area forreinforcement. Not only does this arrangement reduce the mass of themask quite considerably from that of the former ring-mask assembly sothat uniform temperature appears throughout the mask assembly in a veryshort time after the tube is first energized but the strengthening ringon the flange also prevents the translucent area from warping ortwisting to interfere with the passage of the electron beams to the faceof the tube during the warmup period. Even though the mass is reducedthe mask assembly is still rigid enough so Furthermore, masksconstructed in this manner are much lighter in weight and are lesscostly than the mask assemblies which have been used for the most partin the past.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a rear view of the shadowmask for a colored TV picture tube constructed according to theteachings of the invention;

FIG. 2 is a view of the shadow mask from the front;

FIG. 3 is a sectional view taken along viewing line of 33 of FIG. 1;

FIG. 4 is a side elevational view. of an embodiment of the invention;and

FIG. 5 is a sectional view taken along viewing line 5--5 of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The shadow mask of the presentinvention may be of any form suitable for use in picture tubeassemblies, the most general forms being rectangular or circular. Sincethe former is most popular today, the invention will be described asused in producing a rectangular shadow mask.

The mask contains the conventional foraminous or translucent area 10formed by a myriad of miniature apertures which are usually chemicallymilled through a thin sheet of metal, such as stainless steel. In normaluse, when incorporated into the final picture tube as sembly the shadowmask is located near the front viewing face of the picture tube betweenit and the electron guns. When the tube is in operation, the electronbeams are suitably directed through the-translucent area of the mask toimpinge upon the colored phosphor dots on the inside of the face of thepicture tube. The mask is also used during the process for laying downthe color phosphor dots in the conventional triad pattern. Withoutdelving into this process to any great degree, it is merely pointed outthat during the dot-forming steps, the mask ordinarily must be removedand repositioned with respect to the face of the picture tube a numberof times so it is apparent that stability is critical to make sure thatthe tiny apertures return to virtually their exact previous locationeach time the mask is temporarily removed and replaced. It is alsoapparent that temperature stability is quite critical so that thetranslucent area does not shift and interfere with the passage of theelectron beams as they travel from the guns to impinge upon therespective color phosphor dots.

Conventionally, the translucent area 10 is partially domed or curved,usually aspherically, to conform to the curved inner face of the picturetube. Over the years, methods, procedures and equipment have beendeveloped and are today widely known and used throughout the color TVindustry for etching out the translucent area and for curving or shapingthe mask face to the desired contour. These methods, procedures andequipment are not considered part of the present invention.

Around the translucent area is a marginal imperforate area 11 which ismerely a continuation of the same metal sheet but which has not beenetched through. In area 11, near the outer edge of the translucent area10, there is a continuous, inward-projecting, shallow groove 12 whichserves as a strengthening rib for the face area of the aperture mask.This rib is formed in a press using standard techniques. Just a littlebeyond the rib 12, the metal bends backward at about a 90 angle, withrespect to a planar projection of the mask face to form a rearwardextending wall section 13 which, similar to the marginal section 11, ispreferably a further continuation of the same metal sheet. The depth ofdraw to form wall 13 may vary from mask to mask dependingon the size andtype of mask being formed. However, it is referred to in the trade as adeep-drawn mask, as differentiated from a shallowdrawn mask whichordinarily has its wall section extending only a short distancerearward. Typically, with no limitation intended, the wall 13 may be inthe order of l inches deep for an aperture mask used in a 21 or 24 inchpicture tube. Wall 13 contains a continuous groove or strengthening ribwhich strengthens the wall section. Selection of the location and sizeof rib 14 in wall 13 depends on a number of factors, including the sizeof the mask, the depth of the wall, the metal thickness, etc. The choicecan and must be made by the skilled artisan for each application and nodefinite formula to cover all applications appears to be reasonablydeterminable. Investigations have shown that in some instancesadditional ribs, similar to rib 14, may be formed in the wall 13 toprovide some additional strength.

At the rear end of wall 13 the metal sheet is bent inward and formsflange 16 which is approximately at a 90 angle to the wall 13. Flange l6completely encircles the opening at the rear of the mask. Overlayingflange 16 and rigidly attached thereto, such as by welding, is a metalreinforcing ring 17. Preferably, ring 17 is made out of the same metalas the mask. It may be the same thickness as the metal sheet from whichthe mask is formed but for the most part, it has been found preferablethat the ring metal be somewhat thicker, and a thickness in the order oftwice that of the flange has worked very satisfactorily. As a furtherfeature, the inner edge 18 of ring 17 can be flared partially upward forshielding. In addition, as shown in the FIG. 5 embodiment, the ring.17may extend out beyond wall 13 for further shielding to prevent leakageof light and reflection around the outside of the mask between the glassbulb and the mask assembly. It has been found that ring 17 weldedto theflange l6 reinforces the mask to such a degree that the stability andstrength is many times that of the mask without the ring.

Directing attention back to the wall 13, as most clearly seen in FIG. 4and 5, additional strengthening and supporting measures are obtained bypressure formed, shallow, grooved ribs 20 in wall 13. In the embodimentillustrated, these ribs 20 are substantially equally spaced along wall13, are parallel to one another and extend rearward from rib 14 down tothe end of the wall section and further extend at least part way downflange 16. Although this arrangement may be preferable, it iscontemplated and has been shown that variations thereof may and willproduce substantial additional supporting strength and so should beconsidered to come within the spirit and scope of this invention. Forexample, the ribs 20 may not be parallel to one another and/or may be atother than a right angle to rib 14. Here again, the number of ribs 20and the dimensions of the grooves is a matter of design or choicedepending upon many factors such as the dimension and shape of the mask.The practicing artisan can make this choice based upon his experienceand knowledge. Another factor which must be taken into account whendetermining the size and location of the supporting cross ribs 20, aswell as the continuous rib 14, is that these ribs should not interferewith the mounting pads or springs (not shown) which are normallyattached to the wall 14 for the finished mask to the glass bulb.

Tests have shown that masks having reinforcing ring 17 when mounted inpicture tubes show little or no evidence of shift brought about bytemperature differentials and the masks appear to warm up to uniformtemperature in a matter of moments as compared to the 30 to minutesbefore the former ring-mounted assembly was able to reach a fixedtemperature level.

The process steps for fabricating the aperture mask will now bedescribed. Initially, a flat metal sheet, called a blank, which containsthe translucent area formed by chemically milling out the tinyapertures, is annealed to reduce its hardness, to improve itsmachinability, to facilitate cold working, to produce a desiredmicrostructure and to obtain desired mechanical, physical or otherproperties. After annealing, the metal blank is subjected toroller-leveling which is a process whereby the blank is sent over andthrough a series of rollers which break down the molecular structure sothat the metal blank can later be drawn down and formed withoutdistorting or otherwise damaging the miniature apertures. The blank isnext placed in a press where the face of the mask is drawn down to thedesired curvature. All of the steps listed heretofore are commonplaceand have been used in the industry for a considerable period of time andso are not considered a novel part of the prevent invention. Yet theyare necessary steps in the fabrication of masks constructed according tothe teachings of the present invention. 7

During the step of bowing or curving the face of the mask, thestrengthening rib 12 in the face of the mask is formed. Rib 12 may belocated immediately adjacent the outer edge of the translucent area 10or may be located adjacent the corner where wall section 13 meets marginarea 11 or anywhere between. This is a choice which may differ with maskshape, size and other factors. After the curvature and rib 12 have beenformed on.the mask face area, the mask then goes through a second pressoperation to form wall 13. This merely involves drawing down themetal atthe correct angle, about 90, while the face area is heldfirmly in place.An added feature of rib 12 appears during this process step. Because theface area is clamped in position in the area of rib 12, it prevents thedraw-down operation on the wall portion 13 from adversely affecting thecurvature or the hole sizes of the translucent area in the face of themask. It is contemplated that the draw-down of the wall portion may be asingle step operation or may be accomplished by a series of pressoperations. This is a matter of choice and design depending on manyfactors and is determinable by those skilled in press operations andtechniques. There follows another press operation in which rib 14 isformed in side wall 13 and the rear end wall 13 is tucked inward atabout a 90 angle to form flange 16. Finally, ring 17 is placed overflange l6 and welded thereto. Ordinarily, ring 17 is previously cut tosize and is located and held over the flange in a suitable fixture and anumber of welding guns are strategically located to weld the ring ontothe flange. In some cases ring 17 has been found to provide suitablereinforcement when it is the same thickness as the metal sheet fromwhich the rest of the mask is made. In those cases the ring 17 can becut from what otherwise would be scrap metal left over from the unusedportion of the metal sheet. But for the most part, even though ring 17is made from the same metal it is necessary to have it a thicker gaugeto provide the necessary degree of stability. It has been foundpreferable that prior to welding ring 17 to flange 16 the two parts becleaned and run through a furnace for blackening the metal and relievingany stresses and strains. This is a process step which also has beenused in the industry for a number of years and has become quite wellknown. It is contemplated that the parts can be welded together firstand then cleaned and blackened in the special furnace. Here again thesequence is a matter of choice and design depending upon any number ofdifferent factors and can be selected by those familiar with suchfabrication process steps. Lastly, mounting pads or springs must beattached to the outer wall of the shadow mask for use in mounting themask to the inside of the glass envelope. The design and construction ofthe mounting springs is not considered a part of the present inventionnor is the process by which these mounts-are attached. Of course, theyare essential to the overall assembly of the picture tube.

I claim:

1. A method for making an aperture mask for a colored television picturetube mechanically stable, said mask being made out of a single thinsheet of metal and containing a curved translucent area surrounded by animperforate area, said method comprising the steps of:

a. forming a continuous shallow groove in the imperforate area aroundthe translucent area by pressure to form a supporting rib; V

b. drawing down the imperforate area to form a rearward wall around themask;

7 c. forming a continuous shallow groove in said wall by pressure toform a further supporting rib; v

d. bending the free rear edge of said wall -inwardly to form* a flange;and

e. attaching a flat metal reinforcing ring to said flange with the ringin surface to surface contact with the flange.

2. The method as set forth in claim 1 wherein said reinforcing ring isattached to said flange by welding.

1. A method for making an aperture mask for a colored television picturetube mechanically stable, said mask being made out of a single thinsheet of metal and containing a curved translucent area surrounded by animperforate area, said method comprising the steps of: a. forming acontinuous shallow groove in the imperforate area around the translucentarea by pressure to form a supporting rib; b. drawing down theimperforate area to form a rearward wall around the mask; c. forming acontinuous shallow groove in said wall by pressure to form a furthersupporting rib; d. bending the free rear edge of said wall inwardly toform a flange; and e. attaching a flat metal reinforcing ring to saidflange with the ring in surface to surface contact with the flange. 2.The method as set forth in claim 1 wherein said reinforcing ring isattached to said flange by welding.